Lennart Bergelin, who has died at the age of 83, was a big man with a huge smile and a pumping Scandinavian handshake. He was a fine tennis player and a winning Davis Cup captain for Sweden. But he will always be remembered as the man who helped Björn Borg become a sporting icon.

They were together for 12 years as coach and player, from 1971 to 1983; almost father and son. "It's true, he was like a father to me," Borg said on numerous occasions, and although there was hurt when they parted at the end of Borg's triumphant career, the mutual respect, love and admiration between the two men never died.

Once Borg had returned to a normal settled life in Stockholm in the 1990s after a disastrous marriage to an Italian rock star, the two were reconciled. No one needed to remind the five-time Wimbledon and six-time French champion how much he owed to the man who had carried his rackets around the world.

Bergelin never claimed to have discovered Borg or determined his style of play. That accolade rightly goes to Percy Rosberg, who trained the slip of a boy with the shaggy blond hair at the age of 11 and 12. It was Rosberg who told Borg to keep his double-handed backhand, just as it was Rosberg, a few years later, who told Stefan Edberg to get rid of his - decisions that helped to change the course of tennis history.

But Borg came under Bergelin's tutelage by the age of 15 when, as Davis Cup captain, Bergelin decided that Borg should play in a Davis Cup tie against New Zealand. Typically, Bergelin, down to earth and logical as ever, did not fret over a choice that would make Borg the youngest Davis Cup player in history. "I had no one else," Bergelin said simply. "He was already the best player on the team."

And Borg proved it by beating tour veteran Onny Parun in his first singles match. Unsurprisingly, Borg would go on to become the linchpin of the Swedish team and duly led them to victory over Czechoslovakia at Stockholm's Kunglihallen in the 1975 final, with Bergelin supervising from courtside. Apart from apartheid-ostracised South Africa, which had won by default over India the previous year, Sweden had become the first nation outside the big four of the US, Britain, France and Australia to win the Davis Cup in its then 75-year history.

I watched Bergelin's handling of his young charge at tournaments all over the world and was always impressed by the soundness of his judgment. Despite the large age gap, they were good friends who enjoyed an evening on the town together. But Bergelin also knew when to step back and let Borg hit the discos with his friend Vitas Gerulaitis and others.

Nonetheless, as a coach, thoroughness, attention to detail and hard work were paramount. On clay, Borg went through a set of strings in 45 minutes because his rackets were strung so tightly. The man who strung them as the match progressed was Bergelin himself. He ferried Borg's favourite Donnay frames back and forth to the court, not caring if he missed some of the play. His attitude was that, once the match had started, there was nothing more he could do: all the work had been done beforehand.

This was especially true of Borg's preparation for Wimbledon, when the pair of them would hole up in a hotel at Swiss Cottage, north London, and wear out the grass court they hired at the nearby Cumberland Club in the 10 days before the championships. Bergelin brought in sparring partners, but he did much of the hitting himself.

And Borg was never left in any doubt as to how he was doing. You got an instant verdict from Lennart. He was a man who gave it to you straight.

Born in the town of Alingsas, north-east of Gothenburg, Bergelin quickly developed into an exceptional athlete and, at the age of 20, he won the first of nine Swedish national singles titles. As Sweden's first tennis player of true international class, he won 63 out of 83 Davis Cup ties and teamed up with the exiled Czech Jaroslav Drobny to win his sole grand-slam doubles title, the French at Roland Garros in 1948. He captained the Davis Cup team between 1971 and 1976.

In 2006 Bergelin was invited back to the Monte Carlo Country Club, where he had spent months of his life training with Borg, to take part in the tournament's centenary celebrations. He was 80 but still looked as strong as a bull. The former Swedish No 1 Ingrid Lofdahl Bentzer recalls playing mixed doubles with him.

"He hadn't picked up a racket for years because of a painful shoulder," Bentzer said. "And he had had one heart attack and three strokes. So, after about 10 minutes, I suggested he might like to let Robert Haillet, who was on standby, have a go. He just hit another forehand and ignored me. They don't make men like that any more!"

He is survived by his wife, Rose Marie, and three sons.

• Lennart Bergelin, tennis player and coach, born June 10 1925; died November 4 2008